At work, I'm on Windows (2000, the height of Microsoft's operating system line). GDB compiles under mingw with dBUG support if you configure it with --target=m68k-dbug-elf (might want to try compiling under cygwin if it doesn't work, but cygwin is *painfully* slow).
GCC, on the other hand, has *major* problems with cygwin/mingw, so I've been using the pre-compiled mingw binaries from P&E (you can download them for free, in the "starter" development kit, but they come packaged with a crippleware BDM debugger/flasher, code limited to 64k, and a version of newlib that may or may not be modified, so redistributing their binaries is not something I'm prepared to risk) This is just until I can get something compiled myself, of course. Running their binaries with the -v option gives some interesting insights into how they were cross-compiled.
--no need to read below this line, as it has little to do with GDB--
At present, I'm stuck at home on linux, with a cold, so I can't give details about my windows system, but the eventual aim is to distribute a mingw system in a zip file that contains the full source code to gcc, newlib and gdb, and a set of scripts which will reliably compile those tools (so you can edit them if you want), plus pre-compiled binaries as a fall-back for the lazy among us, and a pre-compiled version of eclipse, with example projects (probably based loosely on the public domain dBUG code) which are automatically built by the eclipse Managed Make tool, even when you add new C source files. It will then be up to the community to add support headers etc. for the memory mapped peripherals on different coldfires.
The other possible path is a set of scripts and binaries for use on an x86 system (probably [k]ubuntu dapper, because it's easier to install for new users) with *known* versions of compilers etc. which will perform the same mystical feats. This is likely to be easier to develop for me, and more useful, because I don't have a version of windows lying around at uni, but my sense of ego wants to see this project go cross-platform.
Ambitious? Possibly. Maybe it's the cold talking.